Is It Possible To Fabricate a Nanocomposite with Excellent Mechanical

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Is it possible to fabricate the nanocomposite with excellent mechanical property using unmodified inorganic nanoparticles directly? Chunhua Zhang, Liangjun Xia, Pei Lyu, Yun Wang, Chen Li, Xingfang Xiao, Fangyin Dai, Weilin Xu, Xin Liu, and Bo Deng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 20 Apr 2018 Downloaded from http://pubs.acs.org on April 20, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Is it possible to fabricate the nanocomposite with excellent mechanical property using unmodified inorganic nanoparticles directly? Chunhua Zhang,†,‡,§ Liangjun Xia,†,§,⊥ Pei Lyu,§ Yun Wang,§ Chen Li,§ Xingfang Xiao,§ Fangyin Dai,‡ Weilin Xu,‡,§ Xin Liu,¶,* and Bo Deng,§,¶,* ‡

College of Textiles & Garments, Southwest University, Chongqing 400715, China

§

State Key Laboratory of New Textile Materials and Advanced Processing Technologies,

Wuhan 430073, China ¶

College of Material Science and Engineering, Wuhan Textile University, Wuhan 430073,

China ⊥

Institute for Frontier Materials, Deakin University, Geelong, Victoria 3216, Australia

KEYWORDS: Polyurethane, ZrO2 nanoparticle, aggregate, size distribution, toughening mechanism

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

ABSTRACT: Unmodified ZrO2 nanoparticles (ZDNP) are used for the enhancement of polyurethane (PU) films. Optimized strain and toughness of PU/ZDNP nanocomposite at a 9.09 wt.% ZDNPs are up to 2714.6 %, and 280.78 MJ·m-1, respectively. The unique bimodal ZDNP aggregates size distribution which exploit both interfacial positively and negatively toughening mechanisms accounts mainly for the excellent mechanical property of PU/ZDNP nanocomposite. The dependence of different toughening mechanisms on three sizes of ZDNP aggregates is summarized. These findings provide a new avenue for the industrial production of nanocomposites at low cost without surface modification of inorganic nanoparticles.


2

Page 3 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Rigid inorganic nanoparticles such as TiO2, Al2O3, and ZnO have been widely used in nanocomposites due to their super mechanical properties, excellent corrosion resistance, and good thermal stability

1-4

. However, the high surface energy of these nanoscale fillers produces

aggregates and thus hinders their uniform dispersion in polymer matrix

5-7

. Severely

agglomerated nanoparticles are more likely to cause a poor interfacial adhesion, thus acting as the stress concentration point to weak the mechanical properties of polymers

7,8

. Generally, the

surface modification of nanoparticles was adopted to improve the dispersion stability of nanoparticles in polymer/filler solutions 9. At the same time, the interfacial interaction between the inorganic nanoparticle and the polymer matrix could be enhanced. However, the surface modification of inorganic nanoparticles is complex and costly, which restricts the fabrication of mechanical enhanced polymeric nanocomposite at large scale. Various well-known toughening mechanisms of inorganic nanoparticles to polymers include pull-out 7, crack deflection

10,11

, crack pinning

12

, microcracks

13

, crack bridging

14

, plastic

deformation 15, and plastic void growth 16 were proposed to explain the mechanical enhancement effect of nanoparticles in polymeric nanocomposite. All these toughening mechanisms are proved to be highly correlated with the interfacial force between nanoparticles and polymer matrix

17,18

. Interestingly, the crack deflection, crack pinning, and crack bridging are positively

while the rests are negatively correlated with interfacial force between particles and matrix. That is to say, the former toughing mechanisms take effect at high interfacial force while the latter dominate the mechanical enhancement of the polymeric nanocomposite at low interfacial force. While, narrow size distribution of surface modified nanoparticles inside polymer matrix fixes them solely onto interfacial force positively correlated toughing mechanism due to their unimodal size distribution. As mentioned above, unmodified nanoparticles always suffered from


3


Page 4 of 23

the aggregation due to their high energy level. Another conclusion could be easily drawn out for the unmodified nanoparticles by the evidence that the smaller size of nanoparticles, the bigger interfacial force between them with polymer matrix due to the higher accessible area derived from augmented specific surface area. Taking above-mentioned two points into account, the random aggregation of unmodified nanoparticles may produce a nanoparticle set with wide size distribution spanning interfacial force from low level to high level inside polymeric nanocomposite. In this case, we may enhance the mechanical property of polymer by inorganic nanoparticles without surface decoration. This provides us a more economical and simple choice for the preparation of inorganic nanoparticle enhanced polymeric nanocomposite. In this letter, a cheap and rigid unmodified ZDNP with the diameter of 50 nm were used to prepare PU/ZDNP nanocomposite. The enhancement effect of the concentration of ZDNP on the mechanical property of the nanocomposite was characterized. The size-distribution of ZDNPs in PU matrix were investigated at different ZDNP concentrations using FESEM. Corresponding toughing mechanisms divided into two categories, interfacial force negatively and positively correlated ones, were quantitatively correlated with different sizes of ZDNP aggregates inside PU matrix. Outstanding strain and toughness of 2714.6 % and 280.8 MJ·m-1 of PU/ZDNP nanocomposites could be achieved at the ZDNPs of 9.09 wt.%. Unique bimodal size distribution of the ZDNP summited at both 143.7 nm and 245.0 nm which adopting both interfacial force negatively correlated and positively correlated toughing mechanisms, contribute mutually to the excellent mechanical properties of PU nanocomposite. Represent preparation procedure of PU/ZDNP nanocomposites was depicted as in Figure 1. Detailed experiment conditions could be found in the experiment section in Supporting


4

Page 5 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Information. PU4/ZDNP-9.09 nanocomposites were prepared by a hybrid non-solvent induced phase separation and solvent evaporation (HNIPS-SE) technique. The PU and ZDNPs were firstly added into binary solvents consisting of toluene (TOL) and DMF. After 180 min of mechanical agitation, the bubbles in resulted solution were removed by vacuum degassing for 20 min. Then, obtained PU/ZDNP solution was cast on a glass mold and then the glass mold was kept inside the water coagulation bath at 30 oC for 180 min. Finally, the precipitated PU/ZDNP nanocomposite was oven-dried at 30 oC until constant weight obtained. The as-prepared films were then peeled off the glass mold and conditioned at room temperature for further characterization. The obtained PU/ZDNP nanocomposite is opaque with a white color (Figure 1b). The effect of the ZDNP concentrations on the mechanical properties of PU/ZDNP nanocomposites were systematically investigated by varying the weight percentage of ZDNPs and the volume concentration of TOL according to Table S1 and S2. Prepared PU/ZDNP nanocomposites were then subjected to XRD and mechanical properties characterization (Figure 1). Consistent XRD pattern of ZDNPs inside PU/ZDNP nanocomposite with that of the standard JCPDS-37-1484# reveals a monoclinic ZD inside PU matrix. Broad peak around 21o in the PU/ZDNP nanocomposites is due to the amorphous PU matrix without obvious crystal structure 19. The effects of ZDNP and TOL concentrations on the stress, strain, and toughness of PU/ZDNP nanocomposites, are plotted in Figure S1 (3D surface plots, 2D contour plots), respectively. Increased TOL concentration increases the mechanical properties, including the tensile stress, strain, and toughness, of PU films remarkably until reaching a maximum at the TOL ratio of 40 % (Figure S1). Similar effect of TOL concentration could be observed for PU/ZDNP


5


Page 6 of 23

nanocomposite at a different given ZDNP concentration, including 9.09 %, 16.67 %, 23.07 %, 28.57 % and 33.33%, respectively. Then, the mechanical properties of PU4/ZDNP nanocomposites vs various ZDNPs concentration were investigated. The introduction of ZDNPs significantly improves the strain and toughness of PU film. The values of the strain and toughness of PU/ZDNP nanocomposites reach peak values of 2714.6 ± 146.7 % and 280.8 ± 31.9 MJ·m-3 respectively at the ZDNP concentration of 9.09 % (Figure 1d). Meanwhile, the tensile stress of PU4 nanocomposite only drop down by 3.7 % (from 24.6 ± 1.6 MPa to 23.7 ± 2.0 MPa) after introducing 9.09 % of ZDNPs. As shown in Figure 1d, furtherly increased amount of ZDNP to 33.33 % leads to a significant drop in stress. This decline could be attributed to the severe aggregation due to the high concentration of unmodified ZDNPs 20. Surface morphologies of PU4 (Figure 2c) and PU4/ZDNP-9.09 (Figure 2e) were compared by FESEM. Starting diameter of ZDNPs used for the enhancement of PU4 is 52.5 ± 9.0 nm (Figure 2a and 2b). Different from the dense surface morphology of PU4 film, PU4/ZDNP-9.09 nanocomposite shows some pores spanning from 200 nm to 400 nm, which may due to the detachment of the ZDNP aggregates from PU matrix, implying a poor interfacial interaction between them. After tensile rupture, the dense surface of PU4 could be maintained (Figure 2c and 2d) while the pores on the surface of PU4/ZDNP-9.09 developed into slits along the stretching direction after rupture (Figure 2e and 2f). This pore deformation could be attributed to the stress accumulation induced plastic deformation 21,22. In the FESEM image of fractured PU4/ZDNP-9.09 (Figure 2f), crack paths (indicated by the green ellipse) suggest an interfacial force positively correlated toughening mechanism, such as crack deflection and crack bridging.


6

Page 7 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A few amount of ZDNPs with the diameter of around 50 nm adjacent to the edge of the slit (indicated by the red ellipse) are possibly from pulled-out ZDNP aggregates under external loading. Extra energy could be effectively dissipated by this interfacial force negatively correlated toughening mechanism. Moreover, EDS mapping of PU4/ZDNP-9.09 nanocomposite demonstrates that the density distribution of Zr (indicating ZDNPs) are in good correlated with those of C (indicating PU matrix), indicating a homogeneous distribution of the ZDNPs inside PU matrix. To deeply understand the different toughing mechanisms associated with various ZDNP concentrations, both the brittle fractured (in liquid nitrogen) and tensile fractured cross-sectional images of PU4, PU4/ZDNP-9.09, and PU4/ZDNP-33.33 were compared by FESEM (Figure 3). The brittle fractured cross-sectional FESEM images could provide us with original morphology and size distribution of ZDNP aggregates inside PU matrix at different ZDNP concentrations. Different from the cross-sectional surface of PU4 (Figure 3 a2), two dominating morphologies of ZDNP aggregates, the loosely packed ZDNP aggregates with the diameter of 143.7 ± 32.7 nm and the clover-leaf-shaped ones with the diameter of 244.9 ± 39.1 nm, were homogeneously distributed inside PU4/ZDNP-9.09 nanocomposite (Figure 3 b2). As being widely accepted, shear-induced dispersion and reunion of nanoparticles during blending build a dynamic equilibrium mutually which determines the final size-distribution of nanoparticles inside polymer matrix. High surface activity of unmodified nanoparticles pushes this equilibrium to the reunion side thus hampers the accomplishment of this equilibrium. The reunion tendency of nanoparticles could be regulated by altering their concentrations and consequent different collision frequency. The forming of ZDNP aggregates with different sizes is


7


Page 8 of 23

highly possible in view of the inhomogeneous delivery of shear force inside the whole polymer matrix. Besides, there are several partially pulled out clover-leaf-shaped ZDNP aggregates in PU4/ZDNP-9.09 nanocomposite without stretching (indicated by red circle, Figure 3 b2), which could be due to the difference in the thermal expansion coefficient of the ZDNP (low thermal expansion) with that of the PU (high thermal expansion). Furthermore, severely aggregated ZDNPs (Figure 3 c2) in PU4/ZDNP-33.33 nanocomposite reveals a diameter of 418.0 ± 53.2 nm. The reason for the formed bigger ZDNP aggregates could be due to both increased collision frequency and high surface activity of ZDNP, both facilitate the reunion of ZDNPs. To furtherly clarify the toughening mechanism of ZDNPs associated with their aggregated size, the cross-sectional FESEM images of tensile fractured PU4, PU4/ZDNP-9.09 and PU4/ZDNP-33.33 nanocomposites were compared in Figure 3d-f. Numerous voids are observed in PU4/ZDNP-9.09 nanocomposite (Figure 3 e1) which is associated with interfacial force negatively correlated toughening mechanism. Formation mechanism of these voids is different with those related with thermal expansion in brittle fractured PU4/ZDNP-9.09 nanocomposite (Figure 3 b2). In this case, firstly, external uniaxial stress could be focused and then scattered to different directions by the rigid ZDNP. This stress scattering is due to different modulus and Poisson ratios between rigid ZDNPs and soft PU matrix. Further stretching lead to the shear yielding of soft PU and developed micro-cracks (indicated by green arrows in Figure 3 e2) and thusly grown voids. Reduced contact area between ZDNP aggregates and PU matrix allows the former to be pulled out from the latter due to decreased interfacial force. The fracture energy could be


8

Page 9 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


effectively dissipated via this route which accounts partially to the excellent mechanical properties of PU/ZDNP-9.09 nanocomposite. Additionally, interfacial force positively correlated toughening mechanism such as crack deflection and crack bridging could also be identified in Figure 3 e2 (indicated by yellow arrows). This is another important factor accounting for the he excellent mechanical properties of PU/ZDNP-9.09 nanocomposite. Compared with PU4/ZDNP-9.09 (Figure 3 e1), PU4/ZDNP-33.33 (Figure 3 f1) nanocomposite shows more voids after tensile fracture. To compare the amount of pulled out ZDNPs of PU4/ZDNP-9.09 with that of PU4/ZDNP-33.33, the reduced percentage of Zr after tensile fracture via EDS was calculated and listed in Table 1. Around 1.8 times amount of pulled out ZDNPs of PU4/ZDNP-33.33 than that of PU4/ZDNP-9.09 implied more poor interfacial interaction between aggregated ZDNPs and PU matrix for latter nanocomposite. As mentioned in the brittle fractured FESEM of PU4/ZDNP-33.33, its aggregates reveal a size of 418.0 ± 53.2 nm, which is much bigger than that of PU4/ZDNP-9.09. The augmented size of ZDNP aggregates of PU4/ZDNP-33.33 reduces the accessible area of ZDNPs for PU and thusly promotes the pulling out of ZDNP aggregates from PU matrix. The lacking of microcrack structure in PU4/ZDNP-33.33 further proved its dominate toughening mechanism is pull-out. The stress is more liable to be concentrated by these severely agglomerated ZDNP aggregates which will reduce the breaking strain (Figure 1d). Similar phenomenon was also reported by other authors 2,9,22. More ZDNPs were pulled out from PU4/ZDNP-33.33 than PU4/ZDNP-9.09 after 160 loadingunloading cycles (Figure S4) furtherly proved that ZDNP aggregates with the diameter of 418.0 ± 53.2 nm are more likely to be pulled out than the ZDNP aggregates with the diameter of 244.9 ± 39.1 nm.


9


Page 10 of 23

All in a word, size and size distribution of ZDNP aggregates significantly affect the mechanical properties of PU/ZDNP nanocomposite. Based on the above analysis, two kinds of toughening mechanisms, interfacial force positively and negatively correlated one, are summarized in the table in Figure 4. Three different sizes of ZDNP aggregates are directly linked with corresponding toughening mechanisms. i) ZDNP aggregate with the diameter of 143.7 ± 32.7 nm. Good interfacial adhesion could dissipate the energy via both crack deflection and crack bridging as depicted in right figure of Figure 4a. Crack deflection mechanism proposed by Faber and Evans

23

were ascribed to the effects of the rigid nanoparticle size. The initial main crack

could be stopped or branched by the rigid ZDNPs. In the latter case, cracks passed by the ZDNPs and developed into more cracks with lower energy. Increased fracture surface area could resulted in greater energy absorption as compared to PU4 6. Crack bridging is another general toughening mechanism when the size of ZDNP aggregate is not big enough to branch the major crack 24. ii) Clover-leaf shaped ZDNP aggregates with the diameter of 244.9 ± 39.1 nm. These ZDNP aggregates with poor interfacial adhesion could lead to more microcracks and voids to dissipate more energy, and then improve the toughness of PU/ZDNP nanocomposite. Detailed pulled-out mechanism has been discussed in the tensile fractured FESEM discussion of PU/ZDNP 9.09 already. iii) Severely aggregated ZDNPs with the diameter of 418.0 ± 53.2 nm. Formation of macro voids, and larger cracks is due to larger aggregates size. On one hand, the stress is more easily to be accumulated and thus the fracture energy could be more efficiently


10

Page 11 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dissipated. On the other hand, after the aggregates were completely pulled out from the PU matrix, the remain void with big size are more liable to be broken. In summary, we have prepared a PU/ZDNP nanocomposite with excellent mechanical property using unmodified ZDNPs. Optimized strain and toughness of PU/ZDNP nanocomposite at a 9.09 wt.% ZDNPs are up to 2714.6 %, and 280.78 MJ·m-1, respectively. The unique bimodal ZDNP aggregates size distribution which could exploit both interfacial positively and negatively toughening mechanisms accounts mutually for this excellent mechanical property. The dependence of different toughening mechanisms on three sizes of ZDNP aggregates is summarized. This work provides a new avenue for the industrial production of nanocomposites at low cost with unmodified inorganic nanoparticles.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: Materials, detailed methods and characterization, mechanical properties, and field emission scanning electron microscopy (FESEM) images (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (X.L.). *E-mail: [email protected] (B.D.).


11


Page 12 of 23

Author Contributions †C.Z. and L.X. contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by the China National Funds for Distinguished Young Scholars (grant number 51325306); the National Key Research and Development Program of China (grant number 2016YFA0101102); Excellent Young Science and Technology Innovation Team of Hubei High School (grant number T201707) and the Key Laboratory of Textile Fiber & Product (Wuhan Textile University) (grant number FZXW2017013), Ministry of Education for their financial support. REFERENCES (1) Peterlik, H.; Roschger, P.; Klaushofer, K.; Fratzl, P. From Brittle to Ductile Fracture of Bone. Nat. Mater. 2006, 5 (1), 52-5. (2) Launey, M. E.; Ritchie, R. O. On the Fracture Toughness of Advanced Materials. Adv. Mater. 2009, 21 (21), 2103-2110. (3) Ritchie, R. O. The Conflicts between Strength and Toughness. Nat. Mater. 2011, 10 (11), 817-822. (4) Baradkar, V. P.; Kumar, S. Preparation and Characterization of Epoxy Composites Filled with Functionalized Nanosilica Particles Obtained via Sol–gel Process. Polymer. 2001, 42 (3), 879-887.


12

Page 13 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Mark, J. E.; Lee, Y. C.; Biancini, P. A. In Hybrid Organic-inorganic Composites; Deng, Q., Mauritz, K.A., Moore, R.B. Eds.; American Chemical Society: Washington, DC, 1995; Chapter 7, pp 66-86. (6) Azeez, A. A.; Rhee, K. Y.; Park, S. J.; Hui, D. Epoxy Clay Nanocomposites–processing, Properties and Applications: A Review. Compos. Part B-Eng. 2013, 45 (1), 308-320. (7) Bortz, D. R.; Heras, E. G.; Martingullon, I. Impressive Fatigue Life and Fracture Toughness Improvements in Graphene Oxide/Epoxy Composites. Macromolecules. 2012, 45 (1), 238-245. (8) Chandrasekaran, S.; Sato, N.; Tölle, F.; Mülhaupt, R.; Fiedler, B.; Schulte, K. Fracture Toughness and Failure Mechanism of Graphene Based Epoxy Composites. Compos. Sci. Techno. 2014, 97 (11), 90-99. (9) Wang, X.; Jin, J.; Song, M. An Investigation of the Mechanism of Graphene Toughening Epoxy. Carbon. 2013, 65 (6), 324-333. (10) Rafiee, M. A.; Rafiee, J.; Wang, Z.; Song, H.; Yu, Z. Z.; Koratkar, N. Enhanced Mechanical Properties of Nanocomposites at Low Graphene Content. Acs Nano. 2009, 3 (12), 3884. (11) Deng, S.; Zhang, J.; Lin, Y.; Wu, J. Toughening Epoxies with Halloysite Nanotubes. Polymer. 2008, 49 (23), 5119-5127. (12) Martinez-Rubi, Y.; Ashrafi, B.; Guan, J.; Kingston, C.; Johnston, A.; Simard, B.; Mirjalili, V.; Hubert, P.; Deng, L.; Young, R. J. Toughening of Epoxy Matrices with Reduced Singlewalled Carbon Nanotubes. Acs Appl. Mater. Inter. 2011, 3 (7), 2309-2317.


13


Page 14 of 23

(13) Zhou, Y.; Pervin, F.; Lewis, L.; Jeelani, S. Fabrication and Characterization of Carbon/epoxy Composites Mixed with Multi-walled Carbon Nanotubes. Mat. Sci. Eng. A. 2008, 475 (1–2), 157-165. (14) Ke, W.; Ling, C.; Wu, J.; Toh, M.; He, C.; Yee, A. Epoxy Nanocomposites with Highly Exfoliated Clay: Mechanical Properties and Fracture Mechanisms. Macromolecules. 2005, 38 (3), 788-800. (15) Zhang, K.; Wang, L.; Wang, F.; Wang, G.; Li, Z. Preparation and Characterization of Modified-clay-reinforced and Toughened Epoxy-resin Nanocomposites. J. Appl. Polym. Sci. 2010, 91 (4), 2649-2652. (16) Azeez, A. A.; Rhee, K. Y.; Park, S. J.; Hui, D. Epoxy Clay Nanocomposites–Processing, Properties and Applications: A Review. Compos. Part B-eng. 2013, 45 (1), 308-320. (17) Wetzel, B.; Rosso, P.; Haupert, F.; Friedrich, K. Epoxy Nanocomposites–Fracture and Toughening Mechanisms. Eng. Fract. Mech. 2006, 73 (16), 2375-2398. (18) Biagiotti, J.; Puglia, D.; Torre, L.; Kenny, J. M.; Arbelaiz, A.; Cantero, G.; Marieta, C.; Llano-Ponte, R.; Mondragon, I. A Systematic Investigation on the Influence of the Chemical Treatment of Natural Fibers on the Properties of Their Polymer Matrix Composites. Polym. Composites. 2004, 25 (5), 470-479. (19) Liang, Y. L.; Pearson, R. A. Toughening Mechanisms in Epoxy–silica-nanocomposites (ESNs). Polymer. 2009, 50 (20), 4895-4905.


14

Page 15 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20) Kinloch, A. J.; Mohammed, R. D.; Taylor, A. C.; Eger, C.; Sprenger, S.; Egan, D. The Effect of Silica Nano Particles and Rubber Particles on the Toughness of Multiphase Thermosetting Epoxy Polymers. J. Materials Sci. 2006, 41 (4), 1293-1293. (21) Dittanet, P.; Pearson, R. A. Effect of Silica Nanoparticle Size on Toughening Mechanisms of Filled Epoxy. Polymer. 2012, 53 (9), 1890-1905. (22) Johnsen, B. B.; Kinloch, A. J.; Mohammed, R. D.; Taylor, A. C.; Sprenger, S. Toughening Mechanisms of Nanoparticle-modified Epoxy Polymers. Polymer. 2007, 48 (2), 530-541. (23) Faber, K. T.; Evans, A. G. Crack Deflection Processes-I. Theory. Acta Metal. 1983, 31 (4), 565-576. (24) Qin, Q.; Ye, J. In Toughening Mechanisms in Composite Materials; Shokrieh, M.M., Ghoreishi, S.M., Esmkhani, M., Eds.; Wiley: Sawston, CB, 2015; Chapter 11, pp 295-320.


15


Page 16 of 23

Figure 1. (a) Preparation procedure of PU/ZDNP nanocomposites. (b) Photograph of PU4/ZDNP-9.09 nanocomposites. (c) XRD patterns of ZDNP, PU4 film, PU4/ZDNP-9.09 and PU4/ZDNP-33.33 nanocomposites, respectively. (d) Stress and strain of PU4 film, PU4/ZDNP9.09 and PU4/ZDNP-33.33 nanocomposites, respectively.


16

Page 17 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) FESEM of ZDNP (left), EDS of ZDNP (right). (b) Particle size of ZDNP averaged from (a) using Image-J. (c-f) Surface morphologies of PU4 film and PU4/ZDNP-9.09 nanocomposite before stretching and after tensile fracture: (c1,c2) Low- and high-resolution FESEM images of PU4 (before stretching); (d1,d2) Low- and high-resolution FESEM images of PU4 (after tensile fracture); (e1,e2) Low- and high-resolution FESEM images of PU4/ZDNP-


17


Page 18 of 23

9.09 (before stretching); (f1,f2) Low- and high-resolution FESEM images of PU4/ZDNP-9.09 (after tensile fracture); (g-h) Surface morphologies and the corresponding EDS images of Zr, C, and O elements in PU4/ZDNP-9.09 before stretching (g) and after tensile fracture (h). The white arrows indicate the stretching direction.


18

Page 19 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a-c) Cross-sectional morphologies (brittle fractured surface) of PU4, PU4/ZDNP9.09, and PU4/ZDNP-33.33 nanocomposites, respectively. (a1,a2) Low- and high-resolution FESEM images of PU4 respectively; (b1,b2) Low- and high-resolution FESEM images of


19


Page 20 of 23

PU4/ZDNP-9.09 nanocomposites respectively; (c1,c2) Low- and high-resolution FESEM images of PU4/ZDNP-33.33 nanocomposites respectively. (d-f) Cross-sectional morphologies (tensile fractured surface) of PU4, PU4/ZDNP-9.09, and PU4/ZDNP-33.33 nanocomposites, respectively. (d1,d2)Low- and high-resolution FESEM images of PU4 film; (e1,e2)Low- and high-resolution FESEM images of PU4/ZDNP-9.09 nanocomposites; (f1,f2) Low- and highresolution FESEM images of PU4/ZDNP-33.33 nanocomposites.


20

Page 21 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. ZDNP aggregates size decided toughening mechanisms for different PU/ZDNP nanocomposites. (a) PU4/ZDNP-9.09 nanocomposite: (left) bimodal ZDNP aggregates size distribution and corresponding aggregates morphologies; (right) ZDNP aggregates size selected toughening mechanism. (b) PU4/ZDNP-33.33 nanocomposite: (left) unimodal ZDNP aggregates size distribution and corresponding aggregate morphology; (right) corresponding toughening mechanism.(c) Summarized dependence of different toughening mechanisms on different sizes of ZDNP aggregates.


21


Page 22 of 23

Table 1. The percentages of different elements on the cross-sections of PU4/ZDNP-9.09 and PU4/ZDNP-33.33 nanocomposites via energy dispersive spectrum (EDS). Element content (at.%)a Samples brittle fractured

C

N

O

Zr

51.6

5.1

36.8

6.5

PU4/ZDNP-9.09

Reduced percentage of Zrb

24.6 % tensile fractured

47.2

6.1

41.8

4.9

brittle fractured

29.9

4.9

34.6

30.6

tensile fractured

48.2

3.4

31.8

16.6

PU4/ZDNP-33.33

45.5 %

a: an averaged value from at least five replicates for all samples was taken. b: reduced percentage of Zr was calculated as: (Zrbrittle fractured.

fractured

- Zrtensile

fractured)

×100/Zrbrittle


22

Page 23 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Figure


23

Is It Possible To Fabricate a Nanocomposite with Excellent Mechanical

Recommend Documents